Internally manifolded flow cell for an all-iron hybrid flow battery

ABSTRACT

In one example, a system for a flow cell for a flow battery, comprising: a first flow field; and a polymeric frame, comprising: a top face; a bottom face, opposite the top face; a first side; a second side, opposite the first side; a first electrolyte inlet located on the top face and the first side of the polymeric frame; a first electrolyte outlet located on the top face and the second side of the polymeric frame; a first electrolyte inlet flow path located within the polymeric frame and coupled to the first electrolyte inlet; and a first electrolyte outlet flow path located within the polymeric frame and coupled to the first electrolyte outlet. In this way, shunt currents may be minimized by increasing the length and/or reducing the cross-sectional area of the electrolyte inlet and electrolyte outlet flow paths.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 14/019,491 entitled “INTERNALLY MANIFOLDED FLOW CELL FOR AN ALL-IRONHYBRID FLOW BATTERY”, filed Sep. 5, 2013. U.S. patent application Ser.No. 14/019,491 claims priority to U.S. Provisional Patent ApplicationNo. 61/697,202, entitled “ALL IRON HYBRID FLOW BATTERY”, filed Sep. 5,2012. The present application is also a continuation of U.S. patentapplication Ser. No. 14/019,488, entitled “REDOX AND PLATING ELECTRODESYSTEMS FOR AN ALL-IRON HYBRID FLOW BATTERY”, filed Sep. 5, 2013. U.S.patent application Ser. No. 14/019,488 claims priority to U.S.Provisional Patent Application No. 61/697,202, entitled “ALL IRON HYBRIDFLOW BATTERY”, filed Sep. 5, 2012, and U.S. Provisional PatentApplication No. 61/778,160, entitled “PLATING AND REDOX ELECTRODE SYSTEMAND DESIGN FOR AN ALL IRON REDOX FLOW BATTERY,” filed Mar. 12, 2013. Theentire contents of the above-referenced applications are herebyincorporated by reference for all purposes.

ACKNOWLEDGMENT OF GOVERNMENT SUPPORT

This invention was made with government support under contract no.DE-AR0000261 awarded by the DOE, Office of ARPA-E. The government hascertain rights in the invention.

BACKGROUND AND SUMMARY

The reduction-oxidation (redox) flow battery is an electrochemicalstorage device that stores energy in a chemical form and converts thestored chemical energy to an electrical form via spontaneous reverseredox reactions. The reaction in a flow battery is reversible, soconversely, the dispensed chemical energy may be restored by theapplication of an electrical current inducing the reversed redoxreactions. A single redox flow battery cell generally includes anegative electrode, a membrane barrier, a positive electrode andelectrolytes containing electro-active materials. Multiple cells may becombined in series or parallel to create a higher voltage or current ina flow battery.

Electrolytes are typically stored in external tanks and are pumpedthrough both sides of the battery. When a charge current is applied,electrolytes lose electron(s) at the positive electrode and gainelectron(s) at the negative electrode. The membrane barrier separatesthe positive electrolyte and negative electrolyte from mixing whileallowing ionic conductance. When a discharge current is applied, thereverse redox reactions happen on the electrodes. The electricalpotential difference across the battery is maintained by chemical redoxreactions within the electrolytes and may induce a current through aconductor while the reactions are sustained. During charge, theelectrolytes may be restored to their initial composition for discharge.The amount of energy stored by a redox battery is limited by the amountof electro-active material available in electrolytes for discharge,depending on the total electrolytes volume and the solubility of theelectro-active materials.

Hybrid flow batteries are distinguished by the deposit of one or more ofthe electro-active materials as a solid layer on an electrode. Hybridbatteries may, for instance, include a chemical that forms a solidprecipitate plate on a substrate at some point throughout the chargereaction and may be dissolved by the electrolyte throughout discharge.During charge, the chemical may solidify on the surface of a substrateforming a plate near the electrode surface. Regularly this solidifiedcompound is metallic. In hybrid battery systems, the energy stored bythe redox battery may be limited by the amount of metal plated duringcharge and may accordingly be determined by the efficiency of theplating system as well as the available volume and surface area forplating.

One example of a hybrid redox flow battery uses iron as an electrolytefor reactions wherein on the positive electrode each of two Fe2+ ionseach loses an electron to form Fe3+ during charge, while each of twoFe3+ ions gains an electron to form Fe2+ during discharge. On thenegative electrode, Fe2+ ions receive two electrons and deposit as ironmetal during charge, while iron metal loses two electrons andre-dissolves as Fe2+ during discharge:

2 Fe2+↔Fe3++2e− (Positive/Redox Electrode)

Fe2++2e−↔Fe0 (Negative/Plating Electrode)

However, when multiple flow cells are used in parallel, the cells mustbe hydraulically connected through an electrolyte circulation path. Thiscan be problematic, because these electrolytes are electricallyconductive and therefore shunt current can flow through the electrolytecirculation path cells driven by cell-to-cell voltage differences,causing energy losses and imbalances in the individual charge states ofthe cells.

The inventors herein have devised systems and methods to address theseissues. In one example, a system for a flow cell for a flow battery,comprising: a first flow field; and a polymeric frame, comprising: a topface; a bottom face, opposite the top face; a first side; a second side,opposite the first side; a first electrolyte inlet located on the topface and the first side of the polymeric frame; a first electrolyteoutlet located on the top face and the second side of the polymericframe; a first electrolyte inlet flow path located within the polymericframe and coupled to the first electrolyte inlet; and a firstelectrolyte outlet flow path located within the polymeric frame andcoupled to the first electrolyte outlet. In this way, shunt currents maybe minimized by increasing the length and/or reducing thecross-sectional area of the electrolyte inlet and electrolyte outletflow paths.

In another example a system for a flow cell stack for a flow battery,comprising: two or more electrolyte inlet feeds; two or more electrolyteoutlet feeds; and two or more flow cells, each flow cell comprising: afirst flow field plate; a second flow field plate; and a polymericframe, comprising: a top face; a bottom face; a first side; a secondside, opposite the first side; a first electrolyte inlet located on thetop face and the first side of the polymeric frame; a first electrolyteoutlet located on the top face and the second side of the polymericframe; a first electrolyte inlet flow path located within the polymericframe and coupled to the first electrolyte inlet; a first electrolyteoutlet flow path located within the polymeric frame and coupled to thefirst electrolyte outlet; a second electrolyte inlet located on thebottom face and the first side of the polymeric frame; a secondelectrolyte outlet located on the bottom face and the second side of thepolymeric frame; a second electrolyte inlet flow path located within thepolymeric frame and coupled to the first electrolyte inlet; and a secondelectrolyte outlet flow path located within the polymeric frame andcoupled to the first electrolyte outlet. In this way, the electrolyteinlets and outlets may be separated for each flow cell, thereby managingvoltage differences between cells, decreasing shunt current betweencells, and increasing the performance of the battery.

In yet another example, a system for an all-iron hybrid flow battery,comprising: a redox electrolyte tank including a redox electrolyte; aplating electrolyte tank including a plating electrolyte; and a powermodule coupled to the redox electrolyte tank via a first pump andfurther couple to the plating electrolyte tank via a second pump, thepower module comprising an internally manifolded flow cell stack theinternally manifolded flow cell stack comprising: two or moreelectrolyte feeds connected to the redox electrolyte tank and/or theplating electrolyte tank; a first sub-stack comprising at least a firstflow cells coupled to a first electrolyte feed; and a second sub-stackcomprising at least a second flow cells coupled to a second electrolytefeed. In this way, flow cells with similar voltages may be coupledtogether within a sub-stack, and shunting losses may be minimized byusing separate inlet and outlet ports for each sub-stack.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It will be understood that the summary above is provided to introduce insimplified form a selection of concepts that are further described inthe detailed description, which follows. It is not meant to identify keyor essential features of the claimed subject matter, the scope of whichis defined by the claims that follow the detailed description. Further,the claimed subject matter is not limited to implementations that solveany disadvantages noted above or in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts an example embodiment of a hybrid flowbattery system in accordance with the current disclosure.

FIG. 2 schematically depicts a cross-section of the battery depicted inFIG. 1.

FIG. 3A depicts an example embodiment of a plating electrode inaccordance with the current disclosure.

FIG. 3B depicts a cross section of the plating electrode depicted inFIG. 3A.

FIG. 3C depicts an alternative embodiment of a plating electrode inaccordance with the current disclosure.

FIG. 3D depicts an alternative embodiment of a plating electrode inaccordance with the current disclosure.

FIG. 4A depicts an additional embodiment of a plating electrode inaccordance with the current disclosure.

FIG. 4B depicts a cross section of the plating electrode depicted inFIG. 4A.

FIG. 4C depicts an additional alternate embodiment of a platingelectrode in accordance with the current disclosure.

FIG. 5A schematically depicts a redox plate-electrode assembly inaccordance with the current disclosure.

FIG. 5B shows an example embodiment of a redox plate in accordance withthe current disclosure.

FIG. 6A shows an additional embodiment of a redox plate in accordancewith the current disclosure.

FIG. 6B shows an additional embodiment of a redox plate in accordancewith the current disclosure.

FIG. 6C shows an additional embodiment of a redox plate in accordancewith the current disclosure.

FIG. 7A shows, in schematic detail, an embodiment of a single flow cellin accordance with the current disclosure.

FIG. 7B shows, in schematic detail, a close-up view of a portion of theflow cell of FIG. 7A.

FIG. 8A shows, in schematic detail, an embodiment of a flow cell stackin accordance with the current disclosure.

FIG. 8B shows a diagram of electrolyte flow through the flow cell stackdepicted in FIG. 8A.

FIGS. 3A, 3B, 3C, 3D, 4A, 4B, 4C, 5B, 6A, 6B, 6C, 7A, 7B, and 8A aredrawn to scale, but it should be understood that other dimensions may beused without departing from the scope of this disclosure.

DETAILED SPECIFICATION

The following description relates to systems for an all-iron hybrid flowbattery (IFB), such as the IFB schematically depicted in FIG. 1. The IFBmay include redox and plating electrodes, membrane barriers, and redoxand plating plates, as diagrammed in FIG. 2. The plating electrode maycomprise a folded fin design, as shown in FIGS. 3A, 3B, 3C, 3D, 4A, 4B,and 4C. The plating electrode fins may comprise perforations, as shownin FIGS. 4A and 4C. The redox plate may include a robust polymer plateas well as C/Graphite composite inserts, as shown in FIGS. 5A and 5B.The redox and plating plates may further comprise interdigitated flowfields as shown in FIG. 6A. The flow channels may be stepped as shown inFIG. 6B, or sloped as shown in FIG. 6C. The redox and plating plates maybe included in an internally manifold flow cell, as shown in FIGS. 7Aand 7B. A plurality of flow cells may be assembled into a flow cellstack, as shown in FIG. 8A. The flow cell of FIG. 7A and the flow cellstack of FIG. 8A may facilitate an electrolyte flow pattern that reducesshunt current losses, such as the flow pattern depicted in FIG. 8B.

FIG. 1 shows a schematic diagram of an example embodiment of an all-ironhybrid flow battery (IFB) 100 in accordance with the present disclosure.While not depicted herein, other flow battery configurations may be usedwithout departing from the scope of this disclosure.

IFB 100 comprises a plating electrolyte tank 102, a redox electrolytetank 104, and one or more flow cells 120. Plating electrolyte tank 102may include a plating electrolyte stored within, and redox electrolytetank 104 may include a redox electrolyte stored within. The platingelectrolyte and redox electrolyte may be suitable salts dissolved inwater, such as FeCl2 or FeCl3 (or FeSO4 or Fe2(SO4)3) and othersupporting electrolytes. The plating electrolyte and redox electrolytemay include the same salt at different molar concentrations.

Flow cell 120 may include negative reactor 121 and positive reactor 123.Negative reactor 121 may be fluidly coupled to plating electrolyte tank102 via conduits 113 and 115. Similarly, positive reactor 123 may befluidly coupled to redox electrolyte tank 104 via conduits 114 and 116.Negative reactor 121 may include plating electrode 122. Positive reactor123 may include redox plate 124 and redox electrode 125. Negativereactor 121 and positive reactor 123 may be separated by barrier 126.Barrier 126 may embodied as a membrane barrier, such as an ion exchangemembrane or a microporous membrane, placed between the platingelectrolyte and redox electrolyte to prevent electrolyte cross-over andprovide ionic conductivity.

Components of flow cell 120 are described in further detail herein, andwith regards to FIGS. 2-7. Cross section 200 of flow cell 120 isdescribed herein and shown in FIG. 2.

Plating electrolyte may be accelerated from plating electrolyte tank 102into fluid cell 120 via conduit 113 through the use of pump 130. Platingelectrolyte may then flow back to plating electrolyte tank 102 viaconduit 115. Similarly, redox electrolyte may be accelerated from redoxelectrolyte tank 104 into fluid cell 120 via conduit 114 through the useof pump 132. Redox electrolyte may then flow back to redox electrolytetank 104 via conduit 116.

IFB 100 may also include negative side additive tank 110 and/or positiveside additive tank 112. Additive tanks 110 and 112 may include an acidadditive. Negative side additive tank 110 and positive side additivetank 112 may include different acid additives contained therein, or mayinclude the same acid additive at different concentrations or pH values.Negative side additive tank 110 may be fluidly coupled to negativereactor 121 via conduit 117. In some embodiments, negative side additivetank 110 may be fluidly coupled to plating electrolyte tank 102.Similarly, positive side additive tank 112 may be fluidly coupled topositive reactor 123 via conduit 118, or may be fluidly coupled to redoxelectrolyte tank 104. The negative additive may be accelerated into thenegative reactor 121 by negative additive pump 134. The positive sideadditive may be accelerated into positive reactor 123 by positiveadditive pump 136.

Pumps 130, 132, 134, and 136 may be controlled at least partially by acontrol system 150. Control system 150 may be a microcomputer includingthe following: a microprocessor unit, input/output ports, an electronicstorage medium for executable programs and calibration values (e.g., aread only memory chip), random access memory, keep alive memory, and adata bus. The storage medium read-only memory may be programmed withcomputer readable data representing non-transitory instructionsexecutable by the microprocessor for performing the routines describedbelow as well as other variants that are anticipated but notspecifically listed.

Control system 150 may be configured to receive information from aplurality of sensors, such as sensors 106 and 108, and probes 127 and128, and further configured to send control signals to the pumpsdescribed herein, and/or other actuators within IFB 100, such as one ormore valves. Control system 150 may receive input data from the varioussensors, process the input data, and trigger the pumps and/or otheractuators in response to the processed input data based on instructionor code programmed therein corresponding to one or more routines.

Probe 127 may be disposed within, or otherwise coupled to platingelectrolyte tank 102 in a manner that allows probe 127 to contact theplating electrolyte stored within plating electrolyte tank 102.Similarly, probe 128 may be disposed within, or otherwise coupled toredox electrolyte tank 104 in a manner that allows probe 128 to contactthe redox electrolyte stored within redox electrolyte tank 102. Probes127 and 128 may be used to determine and monitor the chemical propertiesof the electrolytes stored in tanks 102 and 104, respectively.

Sensors 106 and 108 may be disposed within or otherwise coupled toconduits 115 and 116, respectively, in a manner that allows the sensorsto contact electrolyte returning from flow cell 120 to electrolyte tanks102 and 104. Sensors 106 and 108 may determine or monitor chemicalproperties (such as concentration, potential, and pH) of electrolytepassing through conduit 115 and 116, respectively. In some embodiments,sensors 106 and 108 may be optical sensors configured to allow flowthrough of electrolyte.

Some embodiments of IFB 100 may have a plating electrolyte probe,plating electrolyte sensor, redox electrolyte probe, redox electrolytesensor, or some combination thereof. Probes may also be placed insidethe reacting portion of IFB 100 in negative reactor 121 and positivereactor 123.

Data collected from probes 127 and 128, from sensors 106 and 108, andfrom other sensors disposed within IFB 100 may be used by control system150 to control pumps 130, 132, 134, and 136. For example, the flow rateof electrolyte through flow cell 120 may be increased by increasing thespeed of pump 130 and/or pump 132. The pH of electrolyte in flow cell120 and/or electrolyte tanks 102 and 104 may be altered by actuatingpump 134 and/or pump 136. Pumps 130 and 132 may be actuated by controlsystem 150 using different control routines. Similarly, pumps 134 and136 may be actuated by control system 150 using different controlroutines.

Flow cell 120 may be included in a power module (not shown) which may beconnected to a power source, such as a power grid or a renewable powersource. The power source may be used to charge the power module and/orto store electrical energy in the electrolytes. Pumps 130, 132, 134, and136 may be connected to the power module and/or the power source. Thepower module may be discharged through electrical loads, thus releasingelectrical energy stored in the electrolytes.

FIG. 2 shows a schematic diagram of a portion of cross-section 200 ofthe example IFB 100 as described herein and depicted in FIG. 1. Asdescribed with regard to FIG. 1, IFB 100 may include a plurality of flowcells. The flow cells may be aligned in parallel. Cross section 200shows a first flow cell 201 stacked in parallel with a second flow cell251. Only a portion of second flow cell 251 is shown for simplicity. Itshould be understood that multiple parallel flow cells may be appendedto the diagram shown in FIG. 2 to form the flow cell battery of the IFB.

Flow cell 201 may comprise redox plate 205, redox electrode 210, barrier220, and plating electrode 230. As shown in FIG. 2, redox plate 205,redox electrode 210, barrier 220, and plating electrode 230 may bestacked in this order, from the positive electrode to the negativeelectrode. Flow cell 251 may be stacked in parallel with flow cell 201,such that plating electrode 230 is placed adjacent to redox plate 255 offlow cell 251. In the example shown in FIG. 2, plating electrode 230 andredox plate 255 share a face. In some examples, a plating plate or otherbarrier may be placed between the plating electrode of one flow cell andthe redox plate of the adjacent flow cell. An example of this embodimentis described herein and with regards to FIGS. 4A-C.

Redox plates 205 and 255 may comprise a set of channels 207 and 257,respectively. Channels 207 and 257 may facilitate the flow ofelectrolyte through the flow cell. Redox plates 205 and 255 may be madeof a suitable conductive material, such as carbon, graphite or titanium.As discussed further herein, and with reference to FIG. 6A, the redoxplates may be formed of multiple materials, including non-conductivematerials such as plastic in addition to the conductive material.

Redox electrode 210 may be made of a suitable conductive material suchas carbon, graphite, or titanium. Redox electrode 210 may be ahigh-surface electrode, allowing for a relatively largesurface-to-volume ratio, and thus a relatively large reaction area. Theferrous/ferric redox reaction may occur on the surface of redoxelectrode 210.

In embodiments where the redox electrode is made from a carbon material,the carbon material may be electrochemically oxidized to furtherincrease its surface area. The electrochemical oxidizing treatment mayrange from 500 C/g to 5000 C/g depending on the application and thenature of the carbon material. This may have the effect of enhancing theactivity of the electrode due to the increase in surface area, theincrease in O to C molar ratio, as well as the increase in —COOHfunctional groups on the surface. This electrode may be coupled with aset of electrolyte distribution channels to ensure the electrolyte isadministered to the electrode properly. This channel geometry may beselected to ensure the pressure drop is minimized, while maximizing theforced convection through the electrode and minimizing the electricalresistances.

Plating electrode 230 may be made from a suitable substrate material onwhich Fe0 may deposit and solidify during charging. The platingelectrode may use a porous fin structure in order to increase platingkinetics and performance. Examples of plating electrode structure aredescribed herein, and with reference to FIGS. 3A-3D and 4A-4C.Overpotential on the negative electrode side of flow cell 201 may bedecreased by increasing the plating electrode surface area. Further, theperformance of the plating electrode may be increased by reducing theplate thickness and fin height, and thus reducing ohmic losses. Poresize of the plating electrode may be selected to be large enough toprevent blockages from solidified Fe0 during charging. For example, thepore size may be between 0.01 cm and 1 cm, but may be smaller or larger,depending on the storage capacity requirement of the battery. It may beadvantageous to reduce the shared surface area of the redox electrode ofthe flow cell with the plating electrode of the flow cell through themembrane barrier. Plating capacity losses, as a result of ferric ionscrossing over from the redox side and reacting with iron on the platingside may be minimized by allowing for a relatively large volume of openspace within the plating electrode, thus allowing for a high platingdensity (mAh/cm2). The plating material may be made from carbon, iron,iron alloy, stainless steel, titanium, or any suitable material with acarbon, iron, iron alloy, or titanium coating.

Barrier 220 may be a microporous membrane, an ion exchange membrane, ora composite membrane. Barrier 200 may allow for electrical separation ofthe redox electrode and the plating electrode. The membrane may be madefrom a material which prevents crossover of the plating and redoxelectrolytes, and thus low battery coulombic efficiency loss. Themembrane may be made from a material which also provides a high ionicconductivity, and thus low battery performance loss due to membraneresistivity.

Furthermore, to minimize iron corrosion reaction, a pH between 3 and 4is desired for the iron plating reaction on the negative side, whereasto promote redox reaction kinetics, a pH less than 1 is desired for theferrous and ferric ion redox reaction on the positive side. Thus, themembrane may be made from a material which also has a low protoncrossover rate, and that has a high chemical and mechanical stability.

As such, the membrane used in the IFB battery of the current disclosuremay be a microporous membrane that includes a single layer polyolefinseparator (e.g. PP, PE, Polymethylpentene, or similar), laminates of atleast two layers of polyolefins, a cation or anion exchange membrane, orlaminates of microporous polyolefin layers and ion exchange membranes.The microporous polyolefin layers may be further coated or modified toimprove lamination, ion exchange properties, or stability. The laminatesmay be created with pores large enough to accommodate anion or cationspecific resins, beads, or gels to enhance the performance of themembrane.

FIG. 3A shows one example fin structure 300 for a plating electrode inaccordance with the current disclosure. Fin structure 300 comprises afolded, lanced offset (or serrated) fin structure. In the exampledepicted in FIG. 3A, the electrode face is arranged parallel to themembrane barrier (y-z plane) and is immediately adjacent to the platingelectrolyte in the plating side of the cell, as shown in FIG. 2. Theelectrode plate may be plicate such that the cross section of the platein the x-z plane may follow a sinusoidal curve. The cross section (350,see FIG. 3B) of this embodiment is sinusoidally square. As such, a firstplane 301 is closer to the membrane than a second plane 302 that isfurther from the membrane. In this example, both first and second planesare parallel to the membrane.

Linear ridges 320 may run along the surface of the first plane in they-direction at set intervals dividing the plane into strips along they-axis. Alternating strips may be depressed into the second plane sothat two strips may have a congruent edge in the y-z plane but someamount of separation in the x-plane. The separation may be bridged by acrossing ridge 325 connecting the consecutive parallel plate strips atright angles. The fin structure 300 may thus offer increased surfacearea extending along the depth of the oscillations.

The ridges may thus form serrations in the z-direction, furtherincreasing the plate's surface area and allowing electrolyte to flowthrough the fin spacers. A first plane strip and its two adjacent ridgesmay define a fin 340. The second plane strip, separating adjacent fins,may be defined by a plate separator or a fin spacer 341. The finserrations may be aligned along the z-axis such that they are in phasewith the adjacent fins. In other words, the fin offset in thez-direction may occur at the same y-location, be in the same direction,and be offset by the same amount for successive fins.

Fin structure 300 thus has an electrode surface area that extends inthree orthogonal vector directions. The 3-dimensional surface areaconfiguration may increase the surface area without increasing theactive area of the flow battery. The plating electrode material may alsobe porous such that depressions or holes run through or into the plate.In other disclosed embodiments, the plate may be arranged so that it isrotated about the x-axis by 90 degrees such that the ridges run alongthe z-direction. Electrolyte may thus flow in the y-direction, asindicated in FIG. 3 by dashed arrows, or in the z-direction.

The sinusoidally square cross section 350 in the x-z plane depicted inFIG. 3 is shown in greater detail in FIG. 3B. Other embodiments may havesinusoidally triangular or purely sinusoidal cross sections. The crosssection may be defined by a pitch 360, a height 370 and a thickness 380.As shown, pitch 360 is a half wavelength of the sinusoidal crosssection. Height 370 represents the distance between first plane 301 andsecond plane 302. In other words, height 370 represents the depth of thedepressed surface, or the depth of the plating electrode. Height 370 maybe optimized to minimize the plating electrode ohmic resistance loss.Thickness 380 represents the distance from the face adjacent to theelectrolyte to the face opposite the electrolyte. Thickness 380 may beset to the value of the thinnest material allowable, in order tominimize material costs, and to minimize the amount of space used by theplate, thus allowing for more active surface area and plating volume.However, embodiments using iron or an iron alloy as the platingelectrode material may use a thicker electrode in order to increase theplate durability to abate ferric ion attacks on the metal iron surface.In some embodiments, including those where the plating electrode is madefrom iron or an iron alloy, it may be desirable to coat the surface ofthe electrode near the membrane interface with a non-conductive materialsuch as fluoroelastomers (FKM) or perfluourinated elastomers (FFKM) toreduce the ferric ion attack on plated Fe0 from redox side crossover.

Other variations on the disclosed plating electrode may have alternateplicate fin configurations including a herringbone fin, a serrated finwith a triangular profile (narrower on the top and wider on the bottom),a louvered fin, and/or a wavy fin.

FIG. 3C depicts an alternative embodiment of a plating electrode inaccordance with the current disclosure. Plating electrode 385 comprisesa louvered fin design that may comprise one of the cross sectionalpatterns described above with respect to fin structure 300, furtherincluding angled notches protruding from, and along the length of, theridges. The ridges may be sharp (formed by the intersection of twolinear surfaces). The ridges may also be curved and have an archeddownward concavity in the negative x-direction as viewed from the y-zplane alternating with arched upward concavity in the upward x-directionwith maximums at the first plane and minimums in the second plane.

FIG. 3D depicts an alternative embodiment of a plating electrode inaccordance with the current disclosure. Plating electrode 395 comprisesa wavy plicate fin which may comprise a cross-section with a sinusoidalpattern similar to the pattern shown in FIG. 3B. In this embodiment, theridges running along the surface of the first plane in a y-direction maybe separated by an interval dividing the plane into strips along they-axis. Alternating strips may then be depressed into the second planeso that two strips may have a congruent edge in the y-z plane but besome distance apart in the x plane, which may be traversed by a ridgeconnecting the consecutive parallel plates at right angles. In thisembodiment, the fins are displaced sinusoidally in the z-direction.Similar to the previously mentioned embodiments, this configurationallows the electrode surface area a third dimension for expansion sothat surface area may be increased without affecting the active area ofthe cell.

FIG. 4A shows another example fin structure 400 for a plating electrodein accordance with the current disclosure. Fin structure 400 comprises afolded, perforated fin structure. In the example depicted in FIG. 4A,the electrode face is arranged parallel to the membrane barrier and isimmediately adjacent to the plating electrolyte in the plating side ofthe cell, as shown in FIG. 2. The electrode plate may be plicate suchthat the cross section of the plate in the x-z plane may follow asinusoidal curve. The cross section (430, see FIG. 4B) of thisembodiment is sinusoidally trapezoidal. As such, a first plate 405 iscloser to the membrane than a second plate 410 that is further from themembrane. In this example, both first and second plates are parallel tothe membrane and divided into parallel strips. In this example, the sideplates 415 are angled such that strips of second plate 410 have agreater surface area than strips of first plate 405, but it should beunderstood that other configurations are possible without departing fromthe scope of this disclosure. The fins may be constructed out of carbon,iron, iron alloy, stainless steels, or titanium or other base materialsand may be coated with a material such as iron or iron alloy.

Additionally, these fins may also include perforations 417, such asthrough holes, on all surfaces to increase the surface area platingdensity. The perforations are not limited to side plates 415, and insome embodiments perforations may also be included on first plates 405and second plates 410. In some cases it might be advantageous to addperforations to the top plates 405 to reduce the ionic length of finstructure 400. Additionally, these fins may also include perforations417 on all surfaces to increase the surface area plating density.

Other embodiments may have straight linear ridges along the y-or-zdirection dividing the parallel plates into strips; however, they mayshare a ridge axis when viewed from the x-direction. In other words, asshown in FIG. 4B, the width of the strips of first plate 405 is lessthan the separation between adjacent strips in second plate 410. In thisconfiguration, side plates 415 adjoining the top and bottom plate stripsform an obtuse concave upward angle with the second plane and an obtuseconcave downward angle with the first plane.

The fins may also be attached to base plate 420. Base plate 420 may beembodied as a current collector, bipolar plate, etc. and may run along,and adhere to, strips of second plate 410. Base plate 420 may be locatedimmediately adjacent to the plate in the battery and be nearest the backof the redox plate of an adjacent flow battery. The base plate may bemade from carbon, iron, iron alloy, stainless steel, titanium or anysuitable material with a carbon, iron, iron alloy or titanium coating.

The number of fins per inch, or pitch, is defined as the peak-to-peakdistance and defines the density of fins in the electrode. Generally, alarger pitch increases the surface area of the electrode and addssupport to the substrate. If the pitch is too small, themembrane/separator has the potential to sag between the fins. However,the maximum pitch fabricated depends on the tooling available.

FIG. 4B depicts a cross-sectional view 430 of fin structure 400 inconjunction with membrane barrier 435. As shown in FIG. 4B, the width ofeach strip of first plate 405 is indicated at 442, the width of eachstrip of second plate 410 is indicated at 444. The strips of first plate405 are closer to membrane barrier 435 than are the strips of secondplate 410. The ratio of 442 to 444 may, for example, vary from 0.0 to1.0. The ratio may be determined with regard to its proximity frommembrane barrier 435, as ohmic resistance is lower closer to themembrane. Losses may therefore be minimized by embodiments with higher442 to 444 ratios because more Fe0 may deposit closer to membranebarrier 435 where the ohmic resistance may be lower, as opposed tofurther away from the membrane where ohmic resistance may be higher.

If width 442 is greater than width 444, the two plates closer to themembrane may connect with the plated metal during the plating operation,degrading the battery. If this occurs, the ionic path could be cut offcausing a high ohmic resistance. Therefore, disclosed embodiments mayhave a value for width 442 that is smaller than or equal to a value forwidth 444. Typically, plating will occur closer to the membrane, sodisclosed embodiments may maximize the space available for platingcloser to the membrane.

FIG. 4C shows another example fin structure 450 for a plating electrodein accordance with the current disclosure. Fin structure 450 comprisesfeatures of fin structure 400, as well as inter-digitation plates 460and 465. By incorporating inter-digitation plates 460 and 465, finstructure 450 comprises a series of flow channels 470 between the finand the base plate. Flow channels 470 are open on one end and blocked onthe other end. In this way, electrolyte flow may enter one end of thechannel, but may not exit the opposing end. The inter-digitation platesmay force the plating electrolyte to have a better distribution on theplating side. The interdigitation plates may form dead-ended inlet andoutlet flow channels. Similarly, partially interdigitated flow fielddesigns may be used without departing from the scope of this disclosure.Partially interdigitated flow field designs may include constrictedinlet and outlet flow channels, as opposed to dead-ended inlet andoutlet flow channels.

The redox reaction for ferrous/ferric ions on carbon occurs extremelyfast when compared to the plating reaction (approximately 2 orders ofmagnitude). As such, the redox electrode does not limit batteryperformance. However, by pumping electrolytes through graphite flowchannels, as shown in FIG. 2 for example, a number of unnecessaryreactions may occur on the graphite surface of these channels.Eliminating the excess reaction area provided by the graphite surface ofthe channels on the redox plate may reduce the cost of productionwithout effecting battery performance. Furthermore, it is preferable forredox reaction to occur on the high surface redox electrode material,instead of the flow channel, as the ohmic resistance losses at the redoxelectrode are much smaller than the ohmic resistance losses at thechannel.

FIG. 5A shows a redox plate/electrode assembly 500 in which the flowchannels are made from low-cost plastics instead of C/graphite. Redoxplate/electrode assembly 500 may comprise redox plate 505, and redoxelectrode 510. Redox plate 505 may include plastic frame 515, andconductive inserts 520. Plastic frame 515 and conductive inserts 520 maybe assembled to form a plurality of flow channels 530 for the conductionof electrolyte through assembly 500.

Redox electrode 510 may share a first face with a barrier such as amicroporous membrane or ion exchange membrane (not shown) and a secondface with redox plate 550. Redox electrode 510 may be a porouselectrode, as described herein.

Plastic frame 515 may be manufactured from a low-cost plastic, such asPVC or Polyolefin. Plastic frame 515 may be constructed separately fromconductive inserts 520. Plastic frame 515 may be created via machining,injection molding, or compression molding. Conductive inserts 520 may bemanufactured from a material such as carbon, a carbon/graphitecomposite, or titanium, or other material capable of conductingelectrons to and from the ferric/ferrous reaction occurring on the redoxelectrode 510, and capable of withstanding corrosion from ferric orferrous ions. Conductive inserts 520 may form flow ribs when adhered toplastic frame 515, thus providing electrical conductivity forelectrolyte flowing through channels 530. Conductive inserts 520 may beglued to the plastic frame 515 with epoxy, Viton, or other adhesivematerial. Other embodiments may use a mechanical lock-in feature tosecure the conductive inserts to plastic frame 515. Alternately, plasticframe 515 may be formed using injection molding or compression moldingdirectly onto the conductive inserts. Plastic frame 515 may be securedto conductive inserts 520 by mechanical features such as small holes orgroves for liquid plastic to flow into during the molding process whichmay be incorporated into the conductive inserts.

Multiple channels 530 may flow linearly through the redox plate adjacentto the redox electrode that allow electrolyte to pass through redox sideof the IFB. Channels 530 may run parallel or perpendicular to the finsof a disclosed plating electrode. Channels 530 may be direct flowthrough, serpentine, interdigitated, or partially interdigitatedchannels. Examples of channel configurations are described furtherherein and with regards to FIGS. 5B, 6A, 6B, and 6C.

FIG. 5B shows a perspective drawing of a redox plate 550 in accordancewith the current disclosure. Plastic frame 555 is similar to plasticframe 515 depicted in FIG. 5A. However, plastic frame 555 may bemanufactured as part of a larger plastic manifold plate 560.

Flow channels 565 direct electrolyte flows linearly through redox plate550. Conductive inserts 570 provide electrical conductivity when inphysical contact with a redox porous electrode and a plating electrodeof an adjacent cell (not shown). Inserts 570 may each be in the shape ofa rectangular prism with a long edge 575 that may be the length of redoxplate 550. Multiple inserts 570 may be attached to plastic frame 555 sothat they run parallel to an edge and are separated by a distance thatis the width of channels 565. The protruding portion of the plate,referred to as flow ribs 580, may form a second edge 585 of a firstchannel and a first edge 590 of an adjacent second channel. The surfaceof the plate nearest the redox electrode may therefore be sinusoidallysquare.

Conductive plates of significant surface area cannot be constructed outof carbon/graphite composite material using injection molding due to thehigh graphite content, thus the use of plastic plates with C/graphiteinserts allow for high volume manufacturing of redox plates. Further,the use of injection molding allows for greater part-to-part consistencyand lower tolerance than graphite materials. Additionally, the use of alower cost plastic plate material may allow for redox plates to beconstructed at a much lower cost than their C/graphite composite/Ticounterparts.

Bipolar plates may be used in the redox flow battery to direct andtransport electrolytes to the reaction sites and then removed reactedelectrochemical species away from the reaction sites. The flow celldesign of the current disclosure minimizes the three potential batteryperformance loss mechanisms by utilizing forced convection of the pumpedelectrolyte to maximize the electrode active surface area and minimizeohmic resistance. In this way, by utilizing forced convection, freshelectrolyte is ensured to always be on the catalyst surface, theelectrode surface is completely utilized, and any product formation isquickly swept away.

Specifically, the inventors of the current disclosure may employ aninterdigitated or a partially interdigitated flow field design to thefield of redox flow batteries. When a conventional flow field is used,the reactants flow over the surface of the electrode. An interdigitatedflow field, which includes dead-ended inlet and outlet channels, forcesthe incoming reactant to flow through the porous electrode in order toexit. A partially interdigitated flow field, which includes constricted(but not dead-ended) inlet and outlet channels, forces part of theincoming reactant to flow through the porous electrode in order to exitthe flow field. In this way, pressure drops may be managed and balancedthroughout the flow field. This design also converts the transport ofthe reactant and product to and from the catalyst layer from a diffusiondominant mechanism to a forced convection dominant mechanism. As aresult, the diffusion (stagnant) layer in the backing layer of anelectrode may be reduced from the whole backing layer thickness to amuch thinner layer.

FIGS. 6A, 6B, and 6C show embodiments of redox plates that compriseinterdigitated flow field designs. Similar embodiments may be used forpartial interdigitated flow field designs without departing from thescope of this disclosure. Such embodiments may include constricted inletand outlet flow channels, as opposed to dead-ended inlet and outlet flowchannels.

FIG. 6A shows an embodiment of redox plate 600 comprising aninterdigitated flow field 605 in accordance with the present disclosure.In one example, redox plate 600 comprises a plurality of interdigitatedchannels used to distribute fluid. The interdigitated channels include aplurality of alternating dead-ended inlet channels 610 and outletchannels 615 with the same channel depth. The inlet channels 610 andoutlet channels 615 are arranged in an alternating fashion to form theinterdigitated pattern. The channels are separated by ribs 620. Thewidth and depth of the channels and the width of the ribs may be variedto suit the specific embodiment. The use of dead-ended channels forcesthe reactant to flow through the porous electrode.

The redox plate may be manufactured from a material with a high(60-100%) graphite composition or other suitable material. The redoxplate may include a binder composed of any suitable material, includingpolyolefins (PE, PP or others), phenolic, vinyl ester, or other thermalset materials, a thermoplastic (such as PPS, PPSU, PEEK, PTFE, PFA), orother inorganic binding materials. As shown in FIGS. 5A and 5B, thebipolar plate and interdigitated channels may be formed of a robustpolymer while the ribs may be formed of a C/Graphite composite. In thisexemplary design, the channel depths may range from 0.5 to 1.5 mm, butmay be deeper or shallower based on the size and design of the flowcell. The channel/land ratio is defined as the ratio between the widthof the channels and the land, or interchannel distance minus the channelwidth. In this example, the channel width is 1 mm, and the interchanneldistance is 2 mm, yielding a 1 mm land and a 1.0 channel/land ratio. Thechannel width and interchannel distance may be modulated in order toproduce a channel/land ratio for optimal performance for the specificflow cell application. This ratio may fall within the range of 0.5 to3.0 but may be smaller or greater depending on the application.

FIG. 6B shows an alternative embodiment of a redox plate 630 comprisingan interdigitated flow field 635 in accordance with the presentdisclosure. Redox plate 630 may be manufactured similarly to redox plate600. In this embodiment, the inlet channels 640 and outlet channels 645include a series of steps 650 extending from the channel depth 652 tothe plate surface 654. In this example embodiment, there are 8 steps ineach channel, but this number may be increased or decreased to changethe fluid diffusion to optimize performance specific to the application.

FIG. 6C shows yet another embodiment of a redox plate 660 comprising aninterdigitated flow field 665 in accordance with the present disclosure.Redox plate 660 may be manufactured similarly to redox plates 600 and630. In this embodiment, the inlet channels 670 and outlet channels 675are ramped or sloped from the channel depth 677 to the plate surface679. In this embodiment, the fluid is evenly diffused as it enters theactive area into the electrode on the membrane electrode assembly.

One challenge the redox flow battery faces is that all the cells arehydraulically connected through an electrolyte circulation path. Thiscan be problematic as shunt current can flow through the electrolytecirculation path from one series-connected cell to another causingenergy losses and imbalances in the individual charge states of thecells.

Two losses that may be analyzed when building flow cell stacks arepumping losses and shunt current losses. The pumping losses may arisefrom pumping the plating electrolyte and redox electrolyte into and outof the flow cells. The shunting current losses may be due to theelectrolyte being conductive and small shorts developing due to theelectrolyte touching all of the cells. There may be a design to minimizethese two losses and it may be defined as:

min (Σ Shunting Losses+Σ Pumping losses)

In order to reduce the pumping losses, the design requirements may callfor short plumbing lengths with the smallest possible velocity (largehydraulic diameter). However, to reduce the shunting losses, the designmay require long distances between cells and small plumbing areas.

The shunting losses may include at least two different types. The firsttype is due to cell to cell shunting (bipolar plate to bipolar plate).These losses can be significant for large stacks since the losses areadditive:

${\# \; {shunts}} = {2*{\sum\limits_{i = 1}^{{\# \; {cells}} - 1}i}}$

The series is multiplied by two since there may be shunting on the inletand outlet of the cell. The problem may be significantly worse for largestacks. The loss due to shunting is defined by:

${Loss} = \frac{V^{2}}{R}$

Where R is the resistance of the electrolyte between the two cells and Vis the voltage difference between the two cells. To determine the totalshunting loss between the cells in the stack:

${{Cell}\mspace{14mu} {Shunt}\mspace{14mu} {Loss}} = {2*{\sum\limits_{i = 1}^{n - 1}{\sum\limits_{j = i}^{n}\frac{\left( {V_{j} - V_{i}} \right)^{2}}{R_{ij}}}}}$

Where n is the number of cells in the stack. The losses may add upquickly since cell 1 shorts to cells 2, 3, . . . , n and cell 2 shortsto cells 3,4, . . . , n. A larger resistance length, and thereforelarger R, between cells may reduce this loss. This may be accomplishedby adding a dielectric length between each of the bipolar plates. Asmaller cell-to-cell voltage different (Vj-Vi) may also reduce thisloss. This may be accomplished by separating a large stack into multiplesmaller sub-stacks. In accordance with the present disclosure, a plasticframe may be added around the bipolar plate to direct electrolyte flowseparately to different sub-stacks.

In some embodiments of the current disclosure, the resistance from cellto cell may be a function of the electrolyte resistivity, flow channeldimensions and the internal manifolds (both inlet and outlet manifolds).

$R_{ij} = {\rho_{e}\left\lbrack {{2\; \frac{L_{channel}}{A_{channel}}} + {\left( {j - i} \right)*\frac{t_{pf}}{A_{manifold}}}} \right\rbrack}$

Where ρ_(c) is the electrolyte resistivity, L_(channel) is the length ofthe flow channel in the frame and A_(channel) is the area of the channeldefined below. The thickness of the frame is defined as t_(pf) and thearea of the internal manifolds is A_(manifold).

To prevent or reduce such shunt currents, properties of the electrolytesused in an IFB, such as electrical and ionic conductivities, arecharacterized. Based on the above analysis results, shunt currentsbetween cells can be reduced by increasing the ionic resistance betweenflow inlet and outlet ports. This can be achieved by increasing thelength and/or reducing the cross-sectional area of the flow inlet andoutlet paths.

Additionally, cells of similar voltages may be grouped to sub-stacks.Each sub-stack may comprise one or more cells. The inlet and outletchannels for reactants may change positions for each individual cell orsub-stack in order to minimize voltage differences and shunt currentlosses from high voltage cells to low voltage cells. The internalmanifolds may be set up such that there is cascading from each Anode INand Cathode IN, with each cell/sub-stack having reactants in parallel ofother cells/sub-stacks.

FIG. 7A shows an embodiment of an internally manifolded frame 700 for asingle flow cell in accordance with the present disclosure. Internallymanifolded frame 700 may comprise frame 705 and flow field 710. Flowfield 710 may be a redox plate or a plating plate. Internally manifoldedframe 700 may include both redox and plating plates, and both redox andplating electrodes, although only one flow field is shown here. Whenincluded, flow field 710 may be on the top face of internally manifoldframe 700, while the second flow field may be located on the bottomface, opposite the top face of internally manifold frame 700. Asdescribed herein and with regards to FIGS. 5A and 5B, frame 705 may bemanufactured from a robust polymer. Flow field 710 may include flowchannels cast as part of frame 705, and may further include conductiveinserts for electrical conductivity. Flow channels may be interdigitatedor partially interdigitated, and may be sloped or stepped as shown inFIGS. 6A-6C. A plating electrode may be an embodiment of the finstructures as shown in FIGS. 3A-D and 4A-4C.

Frame 705 may include an outer perimeter region 706, and an outer ridge707. Outer perimeter region 706 and outer ridge 707 may not includerouting for electrolyte flow, and may be used to facilitate the stackingof multiple internally manifolded frames into a flow cell stack, asdescribed herein and depicted in FIG. 8A. Frame 705 may further includean inlet/outlet region 708, located interior to outer ridge 707. Frame705 may further include a flow field region 709 located interior toinlet/outlet region 708.

Internally manifolded frame 700 may include several electrolyte inletports 720 a-e and outlet ports 722 a-e located within inlet/outletregion 708. Each frame 700 may include a single inlet port 721 and anoutlet port 731 configured to direct electrolyte flow to and from flowfield 710 via electrolyte flow paths. The remaining ports 720 a-e and722 a-e may be used to direct electrolyte flow to other cells and/orsub-stacks. In the embodiment shown in FIG. 7A, internally manifoldedframe 700 has six inlet ports and six outlet ports, facilitating sixcells or six sub-stacks, but more or fewer inlet and outlet ports may beincluded, depending on the battery design. Internally manifolded frame700 may also include several additional electrolyte inlet ports 723 a-fand additional outlet ports 724 a-f. If flow field 710 is a redox flowfield, a second flow field on the opposite face of frame 705 may be aplating flow field, or vice-versa. As such, if inlet ports 720 a-e and721 route redox electrolyte to frame 705, inlet ports 723 a-f may routeplating electrolyte to frame 705. Similarly to the flow paths shown forflow field 710, one of inlet ports 723 a-f and one of outlet ports 724a-f may be used to route electrolyte to and from a second flow fieldlocated on the opposite face from flow field 710. The remaining inletand outlet ports may route electrolyte to other cells or sub-stackswithin the flow cell stack. The inlet and outlet ports may not belocated within flow field region 709 in order to maintain electrolyteflow path length, as described herein.

In the example shown in FIG. 7A, internally manifold frame 700 comprisesan electrolyte inlet flow path 725 and an electrolyte outlet flow path755. Electrolyte inlet flow path 725 comprises an inlet to manifold port721 where electrolyte enters the manifold, electrolyte inlet flowchannels 730 where electrolyte flows from the inlet port to the inlet ofthe battery, electrolyte inlet flow distribution manifold 735, and aplurality of flow field inlets 736. The inlet to manifold port 721 maybe coupled to an external tube (not shown). Electrolyte inlet flowdistribution manifold 735 may utilize an “ant farm” type of design todistribute electrolyte evenly into flow field 710. Such a configurationis described further herein and with regards to FIG. 7B. Electrolyteinlet flow path 725 may extend around flow field 710 on the border offlow field region 709 and inlet/outlet region 708. In this example,electrolyte inlet flow path 725 includes a first length 725 a extendingfrom inlet port 721 to first bend 726, a second length 725 b extendingfrom first bend 726 and second bend 727, and a third length 725 cextending from second bend 727 to electrolyte inlet flow distributionmanifold 735. Lengths 725 a, 725 b, and 725 c may be continuous andallow electrolyte to flow directly from one to another.

In the example shown in FIG. 7A, electrolyte outlet flow path 755comprises an inlet to manifold port 731 where electrolyte leaves themanifold, electrolyte outlet flow channels 760 where electrolyte flowsfrom the outlet of the battery to the outlet port, electrolyte outletflow distribution manifold 765, and a plurality of flow field outlets766. The outlet to manifold port 731 may be coupled to an external tube(not shown). Electrolyte outlet flow distribution manifold 765 mayutilize an “ant farm” type of design to distribute electrolyte evenlyout of flow field 710. Electrolyte outlet flow path 725 may extendaround flow field 710 on the border of flow field region 709 andinlet/outlet region 708. In this example, electrolyte outlet flow path755 includes a first length 755 a extending from outlet port 731 tofirst bend 757, a second length 755 b extending from first bend 757 tosecond bend 756, and a third length 755 c extending from second bend 756to electrolyte outlet flow distribution manifold 765. Lengths 755 a, 755b, and 755 c may be continuous and allow electrolyte to flow directlyfrom one to another.

Other flow cells sharing a flow cell stack with internally manifoldedframe 700 may use different inlet and outlet ports, and thus requiredifferent electrolyte inlet paths and electrolyte outlet paths. Forexample, internally manifolded frame 700 may be configured to useelectrolyte inlet port 720 e to route electrolyte to the respective flowfield 710 and electrolyte outlet port 722 e to route electrolyte fromflow field 710. In such an example, electrolyte inlet flow path 725would decrease in length. More specifically, the first length 725 a maybe shortened, as it would thus extend from inlet port 720 e to firstbend 726. However, first length 755 a would be extended, as it wouldthus extend from outlet port 722 e to first bend 757. In this way, thecombined inlet and outlet path length may remain the same for eachinternally manifold flow cell within a stack.

FIG. 7B shows an example electrolyte flow path 775 that may beimplemented in the internally manifold frame 700 described herein andwith regards to FIG. 7A. Electrolyte flow path 775 may be the equivalentof electrolyte inlet flow path 725 and/or electrolyte outlet flow path755. Electrolyte flow path 775 may include a port 780, a set of flowchannels 781, and flow distribution manifold 790. Flow distributionmanifold 790 may include a series of junction stages and a series ofmanifold distribution channel sets fluidly coupling the junction stages.In this example, three junction stages are shown, but more or fewer maybe used depending on the flow cell design. In this example, flowdistribution manifold 790 includes first junction stage 782, secondjunction stage 784 and third junction stage 786. Flow distributionmanifold 790 also includes a first set of manifold distribution channels783 coupled between first junction stage 782 and second junction stage784, and a second set of manifold distribution channels 785 coupledbetween second junction stage 784 and third junction stage 786. Thesecond set of manifold distribution channels 785 may include a largernumber of channels than does first set 783. Manifold distributionchannels 785 may have a longer path length than do first set 783. Thirdjunction stage 786 may be coupled to an additional set of manifolddistribution channels, which may be further coupled to additionaljunction stages and additional sets of manifold distribution channels,with electrolyte flow eventually being distributed to a plating or redoxflow field.

In the example where flow distribution manifold 790 is utilized as aninlet flow distribution manifold, electrolyte may enter port 780, whichmay be configured as an electrolyte inlet port. Port 780 may thendistribute electrolyte through electrolyte flow channels 781, which maybe configured as electrolyte inlet flow channels. Electrolyte flowchannels 781 a and 781 b, (and others, where included) may have the samepath length. Electrolyte flow channels 781 may then distributeelectrolyte to first junction stage 782, and then be distributed tofirst set of manifold distribution channels 783. Individual manifolddistribution channels in first set 783 may have the same path length.Electrolyte may then enter second junction stage 784, and then bedistributed to second set of manifold distribution channels 785, andfurther to third junction stage 786.

Individual manifold distribution channels in second set 785 may have thesame path length. For example, distribution channel 785 a may have thesame path length as distribution channel 785 b. However, due to spaceconstraints, channels 785 a and 785 b may have different architecture.As shown, channel 785 a has a single turn, while channel 785 b has afirst and second turn. In this way, pressure drops may be minimized aselectrolyte flows separate and pressure drops to each channel may beequalized by ensuring same electrolyte flow path length and geometries.

In the example where flow distribution manifold 790 is utilized as anoutlet flow distribution manifold, electrolyte may enter third junctionstage 786 and then be distributed to second set of manifold distributionchannels 785. Electrolyte may then flow to second junction stage 784,first set of manifold distribution channels 783, and first junctionstage 782. Electrolyte may then flow to flow channels 781, which may beconfigured as electrolyte outlet flow channels and to port 780, whichmay be configured as an electrolyte outlet port.

FIG. 8A shows an exemplary flow cell stack 800 in accordance with thepresent disclosure. Flow cell stack 800 includes of a plurality of flowcell sub-stacks 810. Each sub-stack may be composed of one or multiplecells. In this example embodiment, the flow channels (or manifolds) arekept fully within the stack, yielding an internally manifolded flow cellstack. In this example, each flow manifold has six sets of identicalflow inlet ports 820 and outlet ports (not shown) aligned but includingdifferent flow inlet and outlet flow paths for redox and platingelectrolytes of different sub-stacks. Each sub-stack 810 includes aninlet port 825 connecting electrolyte flow to a flow field as describedherein and shown in FIG. 7A. Each sub-stack 810 also includes channels830 directing electrolyte flow to other sub-stacks within flow cellstack 800. Electrolyte exiting outlet ports within flow cell stack 800may be combined at a common electrolyte outlet (not shown). As shown inFIG. 7A, each flow cell in the flow cell stack includes an inletelectrolyte path and an outlet electrolyte path. By changing thelocation of the inlet and outlet ports, the lengths of the inletelectrolyte paths and outlet electrolyte paths may change from flow cellto flow cell. In order to maintain the same pressure drop across eachflow cell, the sum of the inlet electrolyte path length and the outletelectrolyte path length may be kept the same for each cell within flowcell stack 800.

FIG. 8B shows an example of fluid flow direction 880 through an IFBstack comprised of six sub-stacks (or six cells). Flow may enter an IFBstack at 385, through inlet ports, such as inlet ports 820 as shown inFIG. 8A. Fluid entering the first port (leftmost, as shown in FIG. 8B)may flow through the inlet manifold port of the first sub-stack, enter aflow field within the sub-stack, and exit an outlet port of the firstsub-stack. Electrolyte may then flow through a channel, bypassing theremaining sub-stacks, and exiting the flow cell stack at 890.

Similarly, fluid entering the second port may flow through a channelbypassing the first sub-stack, then flowing through an inlet manifold ofthe second sub-stack, entering a flow field and exiting from an outletmanifold port. The electrolyte may then flow through a channel,bypassing the remaining sub-stacks and exiting the flow cell stack at890. Similarly, electrolyte may be directed to and from sub-stacks 3-6in this example.

By separating the electrically conductive electrolyte paths, voltagedifferences between cells are managed and shunt current losses betweencells are minimized, thus increasing the performance of the battery.

In accordance with the present disclosure, one way to minimize the cellto cell shunting losses due to the high voltage difference may be tobreak the stack up into smaller stacks or build sub-stacks within asingle stack. Smaller stacks are not cost effective since there would beredundancy on non-repeat parts such as pressure plates and currentcollectors, so internal sub-stacks are assumed in this analysis. Withinternal sub-stacks different electrolyte feeds to and from the stackare employed and each feed provides electrolyte to that specificsub-stack. The shunting loss in this case is defined as:

${{Substack}\mspace{14mu} {Shunt}\mspace{14mu} {Loss}} = {2*{\sum\limits_{i = 1}^{n - 1}{\sum\limits_{j = i}^{n}\frac{\left( {V_{j} - V_{i}} \right)^{2}}{R_{ij}}}}}$

Where n is the number of sub-stacks, V is the sub-stack average voltageand R is the resistance between sub-stacks. As can be seen, it isadvantageous to have a large resistance between sub-stacks. Thisresistance may be obtained by using long external plumbing. In this casethe resistance, Rij, is defined as:

$R_{ij} = {\rho_{e}\left\lbrack {\frac{2*L_{channel}}{\# \; {SS}*A_{channel}} + {2\; \frac{L_{tube}}{A_{tube}}} + {\left( {I + j - 2} \right)\frac{L_{manifold}}{A_{manifold}}}} \right\rbrack}$

Where L_(tube) is the external tube length and A_(tube) is the tubearea.

The pumping losses may be broken up into at least four different areasincluding: inlet and outlet tubing, inlet and outlet internal manifolds,the frame flow channel, and the redox or plating plate. The pressuredrop associated with the redox or plating plate is set due to itsdesign. In an exemplary embodiment where the tubing is circular, thehydraulic diameter of the tubing may be defined as the diameter of thetubing, and the pressure drop in the inlet and outlet tubing andinternal manifolds may be a function of said hydraulic diameter.

The pumping loss is defined as:

${{Pumping}\mspace{14mu} {loss}} = \frac{\Delta \; P*Q}{\eta}$

Where ΔP is the pressure drop in the plumbing (Pa), Q is the flow rate(m³/s) and η is the pump efficiency. The pressure drop is defined fromthe Darcy-Weisbach equation as:

${\Delta \; P} = {\frac{1}{2}*f_{d}*\frac{L}{D_{h}}*\rho*\upsilon^{2}}$

Where f_(d) is the friction factor, L is length (meters), D_(h) is thehydraulic diameter (meters), ρ is the density (kg/m³) and ν is thevelocity of the electrolyte (m/s). The friction factor is calculatedassuming laminar flow by:

$f_{d} = \frac{64}{Re}$

And Re is the Reynolds number defined as:

${Re} = \frac{\upsilon*D_{h}}{\mu}$

Where μ is the kinematic viscosity (m²/s).

When analyzing pumping losses in the frame, circular tubes cannot beassumed since the channels will be added to a flat sheet, so thehydraulic diameter needs to be calculated. To minimize pumping lossesthe perimeter of the channel may be minimized, while maximizing the areaof the channel. In accordance with the present disclosure, a modifiedhalf circle may be machined in the channel. The hydraulic diameter of anon-circular channel may be calculated by:

$D_{h} = \frac{4*A}{P}$

Where A is the cross sectional area of the channel and P is the channelperimeter. In some embodiments a channel width and depth may beallocated. Based on these two variables the optimal hydraulic diametermay be determined for at least the following scenarios:

Type 1: If Channel Depth=Channel Width/2 then

${{Channel}\mspace{14mu} {Area}} = {\frac{\pi}{4}D_{channel}^{2}}$Channel  Perimenter = π * D_(Channel) + W_(Channel)

Type 2: If Channel Depth>Channel Width/2 then

$\mspace{79mu} {{{Channel}\mspace{14mu} {Area}} = {\frac{\pi*W_{channel}^{2}}{16} + {\left( {D_{Channel} - \frac{W_{Channel}}{2}} \right)*W_{Channel}}}}$${{Channel}\mspace{14mu} {Perimenter}} = {{\pi*\frac{W_{Channel}}{2}} + {2*\left( {D_{Channel} - \frac{W_{Channel}}{2}} \right)*W_{Channel}}}$

Type 3: If Channel Depth<Channel Width/2 then

${{Channel}\mspace{14mu} {Area}} = {\frac{\pi*D_{Channel}^{2}}{4} + {\left( {W_{Channel} - D_{Channel}} \right)*D_{Channel}}}$Channel  Perimenter = π * D_(Channel) + (W_(Channel) − D_(Channel)) * W_(Channel)

Depending on the maximum depth constraints of the picture frame, any ofthese or other channel configurations may be used—in order to minimizeboth the pumping losses and shunt current losses.

The systems described herein, and with reference to FIGS. 1, 2, 7A, 7B,8A, and 8B may enable one or more systems. In one example, a system fora flow cell for a flow battery, comprising: a first flow field; and apolymeric frame, comprising: a top face; a bottom face, opposite the topface; a first side; a second side, opposite the first side; a firstelectrolyte inlet located on the top face and the first side of thepolymeric frame; a first electrolyte outlet located on the top face andthe second side of the polymeric frame; a first electrolyte inlet flowpath located within the polymeric frame and coupled to the firstelectrolyte inlet; and a first electrolyte outlet flow path locatedwithin the polymeric frame and coupled to the first electrolyte outlet.The polymeric frame may further comprise: a first inlet flow manifoldlocated within the polymeric frame and coupled between the firstelectrolyte inlet flow path and the first flow field; and a first outletflow manifold located within the polymeric frame and coupled between thefirst electrolyte outlet flow path and the first flow field. The systemmay further comprise a second flow field; and the polymeric frame mayfurther comprise: a second electrolyte inlet located on the bottom faceand the first side of the polymeric frame; a second electrolyte outletlocated on the bottom face and the second side of the polymeric frame; asecond electrolyte inlet flow path located within the polymeric frameand coupled to the first electrolyte inlet; and a second electrolyteoutlet flow path located within the polymeric frame and coupled to thefirst electrolyte outlet. The first electrolyte inlet flow path mayinclude one or more electrolyte inlet flow channels, and the firstelectrolyte outlet flow path includes one or more electrolyte outletflow channels. The one or more electrolyte inlet flow channels and oneor more electrolyte outlet flow channels may have a cross section in theshape of a half-circle or within 10° of a half-circle. A depth of theone or more electrolyte inlet flow channels may be twice a width of theone or more electrolyte inlet flow channels and a depth of the one ormore electrolyte outlet flow channels may be twice a width of the one ormore electrolyte outlet flow channels.

In another example a system for a flow cell stack for a flow battery,comprising: two or more electrolyte inlet feeds; two or more electrolyteoutlet feeds; and two or more flow cells, each flow cell comprising: afirst flow field plate; a second flow field plate; and a polymericframe, comprising: a top face; a bottom face; a first side; a secondside, opposite the first side; a first electrolyte inlet located on thetop face and the first side of the polymeric frame; a first electrolyteoutlet located on the top face and the second side of the polymericframe; a first electrolyte inlet flow path located within the polymericframe and coupled to the first electrolyte inlet; a first electrolyteoutlet flow path located within the polymeric frame and coupled to thefirst electrolyte outlet; a second electrolyte inlet located on thebottom face and the first side of the polymeric frame; a secondelectrolyte outlet located on the bottom face and the second side of thepolymeric frame; a second electrolyte inlet flow path located within thepolymeric frame and coupled to the first electrolyte inlet; and a secondelectrolyte outlet flow path located within the polymeric frame andcoupled to the first electrolyte outlet. In this way, the electrolyteinlets and outlets may be separated for each flow cell, thereby managingvoltage differences between cells and increasing the performance of thebattery. The two or more electrolyte inlet feeds may be coupled to aninlet manifold located within the flow cell stack. The two or moreelectrolyte outlet feeds may be coupled to an outlet manifold locatedwithin the flow cell stack. The two or more electrolyte inlet feeds maybe coupled to an electrolyte tank via an electrolyte pump. The flow cellstack may further comprise two or more sub-stacks, each sub-stackcomprising one or more flow cells. Each sub-stack may be coupled to aseparate electrolyte feed, such that each sub-stack receives electrolyteindependently from all other sub-stacks.

In yet another example, a system for an all-iron hybrid flow battery,comprising: a redox electrolyte tank including a redox electrolyte; aplating electrolyte tank including a plating electrolyte; and a powermodule coupled to the redox electrolyte tank via a first pump andfurther couple to the plating electrolyte tank via a second pump, thepower module comprising an internally manifolded flow cell stack. theinternally manifolded flow cell stack comprising: two or moreelectrolyte feeds connected to the redox electrolyte tank and/or theplating electrolyte tank; a first sub-stack comprising at least a firstflow cells coupled to a first electrolyte feed; and a second sub-stackcomprising at least a second flow cells coupled to a second electrolytefeed. The first sub-stack may further comprise: one or more flow cellscoupled to the first electrolyte feed, the one or more flow cells havingsimilar voltages, the voltages being significantly different from avoltage of the at least one flow cell of the second sub-stack. The oneor more flow cells may further comprise: a first flow field; and apolymeric frame, comprising: a top face; a bottom face, opposite the topface; a first side; a second side, opposite the first side; a firstelectrolyte inlet located on the top face and the first side of thepolymeric frame; a first electrolyte outlet located on the top face andthe second side of the polymeric frame; a first electrolyte inlet flowpath located within the polymeric frame and coupled to the firstelectrolyte inlet; and a first electrolyte outlet flow path locatedwithin the polymeric frame and coupled to the first electrolyte outlet.The one or more flow cells may further comprise: a first inlet flowmanifold located within the polymeric frame and coupled between thefirst electrolyte inlet flow path and the first flow field; and a firstoutlet flow manifold located within the polymeric frame and coupledbetween the first electrolyte outlet flow path and the first flow field.The one or more flow cells may further comprise: a second flow field;and wherein the polymeric frame further comprises: a second electrolyteinlet located on the bottom face and the first side of the polymericframe; a second electrolyte outlet located on the bottom face and thesecond side of the polymeric frame; a second electrolyte inlet flow pathlocated within the polymeric frame and coupled to the first electrolyteinlet; and a second electrolyte outlet flow path located within thepolymeric frame and coupled to the first electrolyte outlet. The firstelectrolyte inlet flow path may include one or more electrolyte inletflow channels, and the first electrolyte outlet flow path includes oneor more electrolyte outlet flow channels. The first electrolyte feed maybe coupled to the first sub-stack via a third pump, and the secondelectrolyte feed is coupled to the second sub-stack via a fourth pump.The redox electrolyte and the plating electrolyte may be FeCl2, FeCl3,FeSO4, or Fe2(SO4)3 solutions.

It will be understood that the systems and methods described herein areexemplary in nature, and that these specific embodiments or examples arenot to be considered in a limiting sense, because numerous variationsare contemplated. Accordingly, the present disclosure includes all noveland non-obvious combinations and sub-combinations of the various systemsand methods disclosed herein, as well as any and all equivalentsthereof.

1. A system for a flow cell stack for a flow battery, comprising a first flow battery cell, the first flow battery cell including: a first flow field; and a polymeric frame, comprising: a top face, a bottom face, opposite the top face, a first side, a second side, opposite the first side, a first electrolyte inlet located on the top face and the first side of the polymeric frame, a first electrolyte outlet located on the top face and the second side of the polymeric frame, a first electrolyte inlet flow path located within the polymeric frame and coupled to the first electrolyte inlet, and a first electrolyte outlet flow path located within the polymeric frame and coupled to the first electrolyte outlet.
 2. The system of claim 1, wherein the polymeric frame further comprises: a first inlet flow manifold located within the polymeric frame and coupled between the first electrolyte inlet flow path and the first flow field; and a first outlet flow manifold located within the polymeric frame and coupled between the first electrolyte outlet flow path and the first flow field.
 3. The system of claim 1, further comprising: a second flow field; wherein the polymeric frame further comprises: a second electrolyte inlet located on the bottom face and the first side of the polymeric frame; a second electrolyte outlet located on the bottom face and the second side of the polymeric frame; a second electrolyte inlet flow path located within the polymeric frame and coupled to the first electrolyte inlet; and a second electrolyte outlet flow path located within the polymeric frame and coupled to the first electrolyte outlet.
 4. The system of claim 2, wherein the first electrolyte inlet flow path includes one or more electrolyte inlet flow channels, and the first electrolyte outlet flow path includes one or more electrolyte outlet flow channels.
 5. The system of claim 4, wherein the one or more electrolyte inlet flow channels and the one or more electrolyte outlet flow channels have a cross section in a shape of a half-circle or within 10° of a half-circle.
 6. The system of claim 5, wherein a depth of the one or more electrolyte inlet flow channels is twice a width of the one or more electrolyte inlet flow channels and wherein a depth of the one or more electrolyte outlet flow channels is twice a width of the one or more electrolyte outlet flow channels.
 7. A system for a flow cell stack for a flow battery, comprising: two or more electrolyte inlet feeds; two or more electrolyte outlet feeds; and two or more flow cells, each flow cell comprising: a first flow field plate; a second flow field plate; and a polymeric frame, comprising: a top face; a bottom face; a first side; a second side, opposite the first side; a first electrolyte inlet located on the top face and the first side of the polymeric frame; a first electrolyte outlet located on the top face and the second side of the polymeric frame; a first electrolyte inlet flow path located within the polymeric frame and coupled to the first electrolyte inlet; a first electrolyte outlet flow path located within the polymeric frame and coupled to the first electrolyte outlet; a second electrolyte inlet located on the bottom face and the first side of the polymeric frame; a second electrolyte outlet located on the bottom face and the second side of the polymeric frame; a second electrolyte inlet flow path located within the polymeric frame and coupled to the first electrolyte inlet; and a second electrolyte outlet flow path located within the polymeric frame and coupled to the first electrolyte outlet.
 8. The system of claim 7, wherein the two or more electrolyte inlet feeds are coupled to an inlet manifold located within the flow cell stack.
 9. The system of claim 7, wherein the two or more electrolyte outlet feeds are coupled to an outlet manifold located within the flow cell stack.
 10. The system of claim 7, wherein the two or more electrolyte inlet feeds are coupled to an electrolyte tank via an electrolyte pump.
 11. The system of claim 7, wherein the flow cell stack further comprises two or more sub-stacks, each sub-stack comprising one or more flow cells.
 12. The system of claim 11, wherein each sub-stack is coupled to a separate electrolyte feed, such that each sub-stack receives electrolyte independently from all other sub-stacks. 13-20. (canceled) 